Which of the following is false regarding medullary carcinoma of the thyroid?
MTC arises from the parafollicular C cells, which produce calcitonin. It's part of the multiple endocrine neoplasia (MEN) syndromes, specifically MEN 2A and 2B. Hereditary forms are associated with RET proto-oncogene mutations. So, any statement that contradicts these points could be false.
Common false statements might include: MTC being a follicular cell tumor (it's C cell), not associated with MEN (it is), not secreting calcitonin (it does), or having a better prognosis than follicular carcinoma (which is not true; MTC has a variable prognosis but is generally more aggressive than some others).
The correct answer would be a statement that's factually incorrect about MTC. For example, if an option says "MTC is a well-differentiated carcinoma of follicular origin," that's false. The explanation should clarify that MTC is from C cells, not follicular. Also, mention RET mutations, calcitonin production, and MEN associations. The clinical pearl could be that MTC is the only thyroid cancer associated with MEN 2 and that surgery is the main treatment.
**Core Concept**
Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor of parafollicular C cells, distinct from follicular-derived thyroid cancers. It is associated with RET proto-oncogene mutations and may occur sporadically or as part of multiple endocrine neoplasia (MEN) 2A/2B syndromes. Key features include calcitonin secretion and amyloid stroma.
**Why the Correct Answer is Right**
The false statement likely claims MTC is a follicular cell-derived tumor. MTC arises from **C cells**, not follicular cells. Sporadic MTC is linked to somatic RET mutations, while familial cases involve germline RET mutations. It produces calcitonin, leading to hypocalcemia via increased renal calcium excretion. Histologically, amyloid deposition (precollagen fragments) is characteristic.
**Why Each Wrong Option is Incorrect**
**Option A:** "MTC is a well-differentiated follicular cell tumor" — Incorrect because MTC originates from **C cells**, not follicular cells.
**Option B:** "MTC is associated with RET proto-oncogene mutations" — Correct; this is a hallmark of both sporadic and familial MTC.
**Option C:** "MTC secretes calcitonin, causing hypercalcemia" — Incorrect; calcitonin **lowers** serum calcium by inhibiting osteoclasts, leading to **hypocalcemia**.
**Option D:** "MTC is the only thyroid cancer associated with MEN syndromes" — Correct; it is linked to MEN 2A and 2B, unlike other thyroid cancers.
**Clinical Pearl / High-Yield Fact**
**MEN 2A** includes MTC, pheoch